U.S. patent number 7,013,143 [Application Number 10/427,120] was granted by the patent office on 2006-03-14 for harq ack/nak coding for a communication device during soft handoff.
This patent grant is currently assigned to Motorola, Inc.. Invention is credited to Amativa Ghosh, Ravi Kuchibhotla, Robert T. Love, Kenneth A. Stewart, Nicholas W. Whinnett.
United States Patent |
7,013,143 |
Love , et al. |
March 14, 2006 |
HARQ ACK/NAK coding for a communication device during soft
handoff
Abstract
A method for rate selection by a communication device for
enhanced uplink during soft handoff in a wireless communication
system includes a first step of receiving information from a
scheduler. This information can include one or more of scheduling,
a rate limit, a power margin limit, and a persistence. A next step
includes determining a data rate for an enhanced uplink during soft
handoff using the information. A next step includes transmitting to
a serving base station on an enhanced uplink channel at the data
rate determined from the determining step.
Inventors: |
Love; Robert T. (Barrington,
IL), Ghosh; Amativa (Buffalo Grove, IL), Kuchibhotla;
Ravi (Gurnee, IL), Stewart; Kenneth A. (Grayslake,
IL), Whinnett; Nicholas W. (Marlborough, GB) |
Assignee: |
Motorola, Inc. (Schaumburg,
IL)
|
Family
ID: |
33310048 |
Appl.
No.: |
10/427,120 |
Filed: |
April 30, 2003 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20040219917 A1 |
Nov 4, 2004 |
|
Current U.S.
Class: |
455/450; 455/442;
455/515; 455/509; 370/341; 370/335 |
Current CPC
Class: |
H04L
1/1671 (20130101); H04L 1/1854 (20130101); H04L
1/1819 (20130101); H04L 1/1861 (20130101); Y02D
30/70 (20200801); H04L 1/0003 (20130101); H04W
36/18 (20130101) |
Current International
Class: |
H04Q
7/20 (20060101) |
Field of
Search: |
;455/450,436,442,458,500,509,517,69,522,67.13
;370/329,341,331,441 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"3.sup.rd Generation Partnership Project; Technical Specification
Group Radio Access Network; Physical Channels and Mapping of
Transport Channels onto Physical Channels (FDD)" 3GPP TS 25.211;
v5.3.0; Dec. 2002. cited by other.
|
Primary Examiner: Feild; Joseph
Assistant Examiner: Afshar; Kamran
Attorney, Agent or Firm: Mancini; Brian M. Vaas; Randall
S.
Claims
What is claimed is:
1. A method in a mobile station for improving uplink performance,
the method comprising the steps of: receiving at least one downlink
ACK/NAK transmission; discriminating between ACK/NAK transmissions
meant for the mobile station and ACK/NAK transmissions meant for
other communication devices by applying coded bits that uniquely
associate ACK/NAK transmissions with the mobile station; and
utilizing the information in the ACK/NAK transmission coded for the
mobile station in determining uplink transmission activity, the
method further comprising the step of using one ACK/NAK channel in
a first set of ACK/NAK channels if a first BTS schedules the mobile
station and optionally using one ACK/NAK channel in a second set of
ACK/NAK channels by the first BTS if other than the first BTS
schedules the mobile station.
2. The method of claim 1, wherein the coded bits are applied to a
field in the downlink physical control channel.
3. The method of claim 1, wherein the coded bits are applied to a
downlink ACK/NAK code channel.
4. The method of claim 3, further comprising the step of allocating
two sets of ACK/NAK channels to each BTS.
5. The method of claim 3, wherein the mobile station includes an
ACK/NAK code channel indicator in an uplink control channel,
wherein only the non-scheduling Active Set BTS's use the ACK/NAK
code channel indicator.
6. The method of claim 3, wherein the mobile station includes an
ACK/NAK code channel indicator in an uplink control channel,
wherein all of the Active Set BTSs use the ACK/NAK code channel
indicator for choosing the appropriate ACK/NAK channel from the
ACK/NAK code channel set.
7. The method of claim 1, wherein the defining step includes
defining second code bits based on a selected scheduling BTS's
unique ID, and the utilizing step includes applying the second code
bits to the uplink communication such that the BTS's can determine
whether it is selected or not.
8. The method of claim 1, wherein the defining step includes the
step of receiving site selection diversity transmit cell ID code
bits, and wherein the utilizing step includes utilizing the cell ID
code bits to indicate which BTS is selected.
9. A method for improving uplink performance for a communication
device in a wireless communication system, the method comprising
steps of: defining coded bits that uniquely identify a particular
communication device; applying the coded bits to a downlink ACK/NAK
transmission in a downlink ACK/NAK code channel that can be
received by a plurality of communication devices; discriminating
between ACK/NAK transmissions meant for the particular
communication device and ACK/NAK transmissions meant for other
communication devices using the coded bits from the applying step;
and utilizing the information in the ACK/NAK transmission coded for
the particular communication device in determining uplink
transmission activity, the method further composing the step of
using one ACK/NAK channel in a first set of ACK/NAK channels if a
first BTS schedules the mobile station and optionally using one
ACK/NAK channel in a second set of ACK/NAK channels by the first
BTS if other than the first BTS schedules the mobile station.
10. The method of claim 9, further comprising the step of
allocating two sets of ACK/NAK channels for each BTS.
11. The method of claim 10, wherein the communication device
includes an ACK/NAK code channel indicator in an uplink control
channel, wherein only the non-scheduling Active Set BTS's use the
ACK/NAK code channel indicator.
12. The method of claim 10, wherein the communication device
includes an ACK/NAK code channel indicator in an uplink control
channel, wherein all of the Active Set BTSs use the ACK/NAK code
channel indicator for choosing the appropriate ACK/NAK channel from
the ACK/NAK code channel set.
13. The method of claim 9, wherein the defining step includes
defining second code bits based on a selected scheduling BTS's
unique ID, and the utilizing step includes applying the second code
bits to the uplink communication such that the BTS's can determine
whether it is selected or not.
14. The method of claim 9, wherein the defining step includes the
step of receiving site selection diversity transmit cell ID code
bits, and wherein the utilizing step includes utilizing the cell ID
code bits to indicate which BTS is selected.
15. A method for improving uplink performance during soft handoff
of a communication device, the method comprising steps of: defining
coded bits that uniquely identify a particular communication
device; applying the coded bits to a downlink ACK/NAK transmission
in a downlink ACK/NAK code channel that can be received by a
plurality of communication devices; discriminating between ACK/NAK
transmissions meant for the particular communication device and
ACK/NAK transmissions meant for other communication devices using
the coded bits from the applying step; allocating two sets of
ACK/NAK channels for at least a first BTS; and using one ACK/NAK
channel in a first set of ACK/NAK channels to communicate with the
first BTS if the first BTS schedules the communication device and
optionally using one ACK/NAK channel in a second set of ACK/NAK
channels to communicate with the first BTS if other than the first
BTS schedules the communication device.
16. The method of claim 15, wherein the communication device
includes an ACK/NAK code channel indicator in an uplink control
channel, wherein only the non-scheduling Active Set BTS's use the
ACK/NAK code channel indicator.
17. The method of claim 15, wherein the defining step includes
defining second code bits based on a selected scheduling BTS's
unique ID, and the utilizing step includes applying the second code
bits to the uplink communication such that the BTS's can determine
whether it is selected or not.
18. The method of claim 15, wherein the defining step includes the
step of receiving site selection diversity transmit cell ID code
bits, and wherein the utilizing step includes utilizing the cell ID
code bits to indicate which BTS is selected.
19. A method for improving uplink performance for a first
communication device during soft handoff in a communication system,
the method comprising steps of: receiving ACK/NAK transmissions in
a downlink ACK/NAK code channel; discriminating between ACK/NAK
transmissions meant for the first communication device and ACK/NAK
transmissions meant for other communication devices using coded
bits that uniquely identify the particular communication device;
receiving an allocation of two sets of ACK/NAK channels for a first
base station; and using one ACK/NAK channel in a first set of the
two sets of ACK/NAK channels if the first base station schedules
the first communication device and optionally using one ACK/NAK
channel in a second set of the two sets of ACK/NAK channels if
other than the first base station schedules the first
communications device.
Description
FIELD OF THE INVENTION
The present invention relates generally to a wireless communication
device, and more specifically to soft handoff combining hybrid
automatic repeat request (ARQ).
BACKGROUND OF THE INVENTION
In a Universal Mobile Telecommunications System (UMTS), such as
that proposed for the next of the third generation partnership
project (3GPP) standards for the UMTS Terrestrial Radio Access
Network (UTRAN), such as wideband code division multiple access
(WCDMA) or cdma2000 for example, user equipment (UE) such as a
mobile station (MS) communicates with any one or more of a
plurality of base station subsystems (BSSs) dispersed in a
geographic region. Typically, a BSS (known as Node-B in WCDMA)
services a coverage area that is divided up into multiple sectors
(known as cells in WCDMA). In turn, each sector is serviced by one
or more of multiple base transceiver stations (BTSs) included in
the BSS. The mobile station is typically a cellular communication
device. Each BTS continuously transmits a downlink pilot signal.
The MS monitors the pilots and measures the received energy of the
pilot symbols.
In a typical cellular system, there are a number of states and
channels for communications between the MS and the BSS. For
example, in IS95, in the Mobile Station Control on the Traffic
State, the BSS communicates with the MS over a Forward Traffic
Channel in a forward link and the MS communicates with the BSS over
a Reverse Traffic Channel in a reverse link. During a call, the MS
must constantly monitor and maintain four sets of pilots. The four
sets of pilots are collectively referred to as the Pilot Set and
include an Active Set, a Candidate Set, a Neighbor Set, and a
Remaining Set, where, although the terminology may differ, the same
concepts generally apply to the WCDMA system.
The Active Set includes pilots associated with the Forward Traffic
Channel assigned to the MS. This set is active in that the pilots
and companion data symbols associated with this set are all
actively combined and demodulated by the MS. The Candidate Set
includes pilots that are not currently in the Active Set but have
been received by the MS with sufficient strength to indicate that
an associated Forward Traffic Channel could be successfully
demodulated. The Neighbor Set includes pilots that are not
currently in the Active Set or Candidate Set but are likely
candidates for handoff. The Remaining Set includes all possible
pilots in the current system on the current frequency assignment,
excluding the pilots in the Neighbor Set, the Candidate Set, and
the Active Set.
When the MS is serviced by a first BTS, the MS constantly searches
pilot channels of neighboring BTSs for a pilot that is sufficiently
stronger than a threshold value. The MS signals this event to the
first, serving BTS using a Pilot Strength Measurement Message. As
the MS moves from a first sector serviced by a first BTS to a
second sector serviced by a second BTS, the communication system
promotes certain pilots from the Candidate Set to the Active Set
and from the Neighbor Set to the Candidate Set. The serving BTS
notifies the MS of the promotions via a Handoff Direction Message.
Afterwards, for the MS to commence communication with a new BTS
that has been added to the Active Set before terminating
communications with an old BTS, a "soft handoff" will occur.
For the reverse link, typically each BTS in the Active Set
independently demodulates and decodes each frame or packet received
from the MS. It is then up to a switching center or selection
distribution unit (SDU) normally located in a Base Station Site
Controller (BSC), which is also known as a Radio Network Controller
(RNC) in WCDMA terminology, to arbitrate between the each BTS's
decoded frames. Such soft handoff operation has multiple
advantages. Qualitatively, this feature improves and renders more
reliable handoff between BTSs as a user moves from one sector to
the adjacent one. Quantitatively soft-handoff improves the
capacity/coverage in a cellular system. However, with the
increasing amount of demand for data transfer (bandwidth), problems
can arise.
Several third generation standards have emerged, which attempt to
accommodate the anticipated demands for increasing data rates. At
least some of these standards support synchronous communications
between the system elements, while at least some of the other
standards support asynchronous communications. At least one example
of a standard that supports synchronous communications includes
cdma2000. At least one example of a standard that supports
asynchronous communications includes WCDMA.
While systems supporting synchronous communications can sometimes
allow for reduced search times for handover searching and improved
availability and reduced time for position location calculations,
systems supporting synchronous communications generally require
that the base stations be time synchronized. One such common method
employed for synchronizing base stations includes the use of global
positioning system (GPS) receivers, which are co-located with the
base stations that rely upon line of sight transmissions between
the base station and one or more satellites located in orbit around
the earth. However, because line of sight transmissions are not
always possible for base stations that might be located within
buildings or tunnels, or base stations that may be located under
the ground, sometimes the time synchronization of the base stations
is not always readily accommodated.
However, asynchronous transmissions are not without their own set
of concerns. For example, the timing of uplink transmissions in an
environment supporting MS-autonomous scheduling (whereby a MS may
transmit whenever the MS has data in its transmit buffer and all
MSs are allowed to transmit as needed) by the individual MSs can be
quite sporadic and/or random in nature. While traffic volume is
low, the autonomous scheduling of uplink transmissions is less of a
concern, because the likelihood of a collision (i.e. overlap) of
data being simultaneously transmitted by multiple MSs is also low.
Furthermore, in the event of a collision, there are spare radio
resources available to accommodate the need for any
retransmissions. However, as traffic volume increases, the
likelihood of data collisions (overlap) also increases. The need
for any retransmissions also correspondingly increases, and the
availability of spare radio resources to support the increased
amount of retransmissions correspondingly diminish. Consequently,
the introduction of explicit scheduling (whereby a MS is directed
by the network when to transmit) by a scheduling controller can be
beneficial.
However even with explicit scheduling, given the disparity of start
and stop times of asynchronous communications and more particularly
the disparity in start and stop times relative to the start and
stop times of different uplink transmission segments for each of
the non-synchronized base stations, gaps and overlaps can still
occur. Both data gaps and overlaps represent inefficiencies in the
management of radio resources (such as rise over thermal (ROT), a
classic and well-known measure of reverse link traffic loading in
CDMA systems), which if managed more precisely can lead to more
efficient usage of the available radio resources and a reduction in
the rise over thermal (ROT).
For example, FIG. 1 is a block diagram of communication system 100
of the prior art. Communication system 100 can be a cdma2000 or a
WCDMA system. Communication system 100 includes multiple cells
(seven shown), wherein each cell is divided into three sectors (a,
b, and c). A BSS 101 107 located in each cell provides
communications service to each mobile station located in that cell.
Each BSS 101 107 includes multiple BTSs, which BTSs wirelessly
interface with the mobile stations located in the sectors of the
cell serviced by the BSS. Communication system 100 further includes
a radio network controller (RNC) 110 coupled to each BSS and a
gateway 112 coupled to the RNC. Gateway 112 provides an interface
for communication system 100 with an external network such as a
Public Switched Telephone Network (PSTN) or the Internet.
The quality of a communication link between an MS, such as MS 114,
and the BSS servicing the MS, such as BSS 101, typically varies
over time and movement by the MS. As a result, as the communication
link between MS 114 and BSS 101 degrades, communication system 100
provides a soft handoff (SHO) procedure by which MS 114 can be
handed off from a first communication link whose quality has
degraded to another, higher quality communication link. For
example, as depicted in FIG. 1, MS 114, which is serviced by a BTS
servicing sector b of cell 1, is in a 3-way soft handoff with
sector c of cell 3 and sector a of cell 4. The BTSs associated with
the sectors concurrently servicing the MS, that is, the BTSs
associated with sectors 1-b, 3-c, and 4-a, are known in the art as
the Active Set of the MS.
Referring now to FIG. 2, a soft handoff procedure performed by
communication system 100 is illustrated. FIG. 2 is a block diagram
of a hierarchical structure of communication system 100. As
depicted in FIG. 2, RNC 110 includes an ARQ function 210, a
scheduler 212, and a soft handoff (SHO) function 214. FIG. 2
further depicts multiple BTSs 201 207, wherein each BTS provides a
wireless interface between a corresponding BSS 101 107 and the MSs
located in a sector serviced by the BSS.
When performing a soft handoff, each BTS 201, 203, 204 in the
Active Set of the MS 114 receives a transmission from MS 114 over a
reverse link of a respective communication channel 221, 223, 224.
The Active Set BTSs 201, 203, and 204 are determined by SHO
function 214. Upon receiving the transmission from MS 114, each
Active Set BTS 201, 203, 204 demodulates and decodes the contents
of a received radio frame along with related frame quality
information.
At this point, each Active Set BTS 201, 203, 204 then conveys the
demodulated and decoded radio frame to RNC 110, along with related
frame quality information. RNC 110 receives the demodulated and
decoded radio frames along with related frame quality information
from each BTS 201, 203, 204 in the Active Set and selects a best
frame based on frame quality information. Scheduler 212 and ARQ
function 210 of RNC 110 then generate control channel information
that is distributed as identical pre-formatted radio frames to each
BTS 201, 203, 204 in the Active Set. The Active Set BTSs 201, 203,
204 then simulcast the pre-formatted radio frames over the forward
link. The control channel information is then used by MS 114 to
determine what transmission rate to use.
Alternatively, the BTS of the current cell where the MS is camped
(BTS 202) can include its own scheduler and bypass the RNC 110 when
providing scheduling information to the MS. In this way, scheduling
functions are distributed by allowing a mobile station (MS) to
signal control information corresponding to an enhanced reverse
link transmission to active set base transceiver stations (BTSs)
and by allowing the BTSs to perform control functions that were
previously supported by a RNC. The MS in a SHO region can choose a
scheduling assignment corresponding to a best Transport Format and
Resource Indicator (TFRI) out of multiple scheduling assignments
that the MS receives from multiple Active Set BTS. As a result, the
enhanced uplink channel can be scheduled during SHO, without any
explicit communication between the BTSs. In either case, explicit
transmit power constraints (which are implicit data rate
constraints) are provided by a scheduler, which are used by the MS
114, along with control channel information, to determine what
transmission rate to use.
As proposed for the UMTS system, a MS can use an enhanced uplink
dedicated transport channel (EUDCH) to achieve an increased uplink
data rate. The MS must determine the data rate to use for the
enhanced uplink based on local measurements at the MS and
information provided by the scheduler or UTRAN. Moreover, to
achieve higher throughput on the reverse link, communication
systems such as communication system 100 have adapted techniques
such as Hybrid Automatic Repeat ReQuest (H-ARQ) and Adaptive
Modulation and Coding (AMC), as are known in the art.
Adaptive Modulation and Coding (AMC) provides the flexibility to
match the modulation and forward error correction (FEC) coding
scheme to the current channel conditions for each user, or MS,
serviced by the communication system. AMC promises a large increase
in average data rate for users that have a favorable channel
quality due to their proximity to a BTS or other geographical
advantage. Enhanced GSM systems using AMC offer data rates as high
as 384 kbps compared to 100 kbps without AMC. Likewise, 5 MHz CDMA
systems can offer downlink and uplink peak data rates as high as 10
Mbps and 2 Mbps respectively through AMC, where 2 Mbps and 384 kbps
was typical without AMC.
AMC has several drawbacks, however. AMC is sensitive to channel
quality measurement error and delay. More precisely, in order to
select the appropriate modulation, the scheduler, such as scheduler
212, must be aware of the channel quality. Errors in the channel
estimate will cause the scheduler to select the wrong data rate and
either transmit at too high a power level, wasting system capacity,
or too low a power level, raising the block error rate. Delay in
reporting channel measurements also reduces the reliability of the
channel quality estimate due to constantly varying mobile channel.
To overcome measurement delay, the frequency of channel measurement
reporting may be increased. However, an increase in measurement
report rate consumes system capacity that otherwise might be used
to carry data.
Hybrid ARQ is an implicit link adaptation technique. Whereas, in
AMC explicit C/I measurements or similar measurements are used to
set the modulation and coding format, in H-ARQ, link layer
acknowledgements are used for re-transmission decisions. Many
techniques have been developed for implementing H-ARQ, such as
Chase combining, Rate Compatible Punctured Turbo codes, and
Incremental Redundancy. Incremental Redundancy, or H-ARQ-type-II,
is an implementation of the H-ARQ technique wherein instead of
sending simple repeats of the entire coded packet, additional
redundant information is incrementally transmitted if the decoding
fails on the first attempt.
H-ARQ-type-III also belongs to the class of Incremental Redundancy
ARQ schemes. However, with H-ARQ-type-III, each retransmission is
self-decodable, which is not the case with H-ARQ-type II. Chase
combining (also called H-ARQ-type-III with one redundancy version)
involves the retransmission by the transmitter of the same coded
data packet. The decoder at the receiver combines these multiple
copies of the transmitted packet weighted by the received SNR.
Diversity (temporal) gain as well as coding gain (for IR only) is
thus obtained after each re-transmission. In H-ARQ-type-III with
multiple redundancy, different puncture bits are used in each
retransmission. The details for how to implement the various H-ARQ
schemes are commonly known in the art and therefore are not
discussed herein.
H-ARQ combined with AMC can greatly increase user throughputs,
potentially doubling or even trebling system capacity. In effect,
Hybrid ARQ adapts to the channel by sending additional increments
of codeword redundancy, which increases the coding rate and
effectively lowers the data rate to match the channel. Hybrid ARQ
does not rely only on channel estimates but also relies on the
errors signaled by the ARQ protocol. In both cdma2000 and WCDMA
systems, the reverse link ARQ function, such as ARQ function 210,
and a scheduling function, such as scheduling function 212, can
reside in an RNC 110 or distributed within the BTSs, which can
better support soft handoffs, avoiding latencies inherent when
scheduling through the RNC.
Efficient layer 1 signaling is needed to enable fast explicit and
autonomous (implicit) scheduling with (Stop & Wait) Hybrid ARQ
at the BTS for the enhanced uplink. To enable uplink Hybrid ARQ an
acknowledged/not acknowledged (ACK/NAK) feedback code channel can
be used. During soft handoff an MS is told by a scheduling BTS
which downlink code channel it should listen to for receiving
ACK/NAK information. However, the MS does not know which code
channel to listen to from the other non-scheduling Active Set
BTS's. Also, since there is no coordination between BTSs, the
information sent by a scheduling Active Set BTS is not known to the
other Active Set BTSs which poses a problem when soft combining of
multi-cast signals from different Active Set BTSs. Without the
ACK/NAK feedback information from the other non-scheduling Active
Set BTS's no macro selection diversity benefit is obtained.
Therefore, a need exists for a new technique for HARQ ACK/NAK
coding for a communication device during soft handoff. This coding
should provide feedback information from the non-scheduling Active
Set BTS's to the MS such that a macro selection diversity benefit
is obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the present invention, which are believed to be
novel, are set forth with particularity in the appended claims. The
invention, together with further objects and advantages thereof,
may best be understood by reference to the following description,
taken in conjunction with the accompanying drawings, in the several
figures of which like reference numerals identify like elements,
and in which:
FIG. 1 is a block diagram of an exemplary communication system of
the prior art;
FIG. 2 is a block diagram of a hierarchical structure of the
communication system of FIG. 1;
FIG. 3 depicts a distributed network architecture in accordance
with an embodiment of the present invention;
FIG. 4 is a block diagram of a communication system in accordance
with an embodiment of the present invention;
FIG. 5 is a message flow diagram in accordance with an embodiment
of the present invention;
FIG. 6 is an exemplary illustration of a ACK/NAK coloring for BPSK
modulation, in accordance with the present invention;
FIG. 7 is an exemplary illustration of a ACK/NAK coloring for QPSK
modulation, in accordance with the present invention;
FIG. 8 is a timing diagram in accordance with the present
invention;
FIG. 9 is a prior art timing diagram for a DPCH; and
FIG. 10 is a timing diagram for a second embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides new techniques for HARQ ACK/NAK
coding for a communication device during soft handoff. This coding
allows the MS to properly utilize feedback information from
non-scheduling Active Set BTS's to the MS such that a macro
selection diversity benefit is obtained.
Soft-handoff on the reverse link (from the mobile station (MS) to
the base station (BTS)) is an essential component of any UMTS
system. Typically, the BTSs in soft handoff will decode packets or
frames (hereinafter referred to as frames) transmitted by the MS.
There can be a maximum of six base stations in soft handoff. The
quality information on the decoded frames is transmitted from the
BTS up to the Radio Network Controller (RNC) or Selection
Distribution Unit (SDU). The RNC selects the frame received from
the BTS with the highest quality. Quantitatively, soft-handoff
improves the capacity/coverage in a CDMA system.
The present invention supports Active Set handoff and scheduling
functions by allowing a mobile station (MS) to provide HARQ ACK/NAK
coding information to improve data throughput of an enhanced
reverse link transmission to Active Set base transceiver stations
(BTSs). The present invention allows more efficient implementation
of an enhanced reverse link channel with adaptive modulation and
coding (AMC), Hybrid ARQ (HARQ), and fast scheduling with reduced
ARQ delay. HARQ, AMC, Active Set handoff, and scheduling functions
are preferably supported in a distributed fashion by allowing a
mobile station (MS) to signal control information corresponding to
an enhanced reverse link transmission to Active Set base
transceiver stations (BTSs) and by allowing the BTSs to perform
control functions. Time and signal-to-noise ratio (SNR)-based HARQ
flush functions are supported at the BTSs during soft handoff
(SHO), and provides an efficient control channel structure to
support scheduling, HARQ, AMC functions for an enhanced reverse
link, or uplink, channel in order to maximize throughput, and
enables an MS in a SHO region to choose a scheduling assignment
corresponding to a best transport format and resource-related
information (TFRI) out of multiple scheduling assignments that the
MS receives from multiple Active Set BTS. As a result, the enhanced
uplink channel can be scheduled during SHO, while supporting HARQ
and AMC, without any explicit communication between the BTSs.
Generally, an embodiment of the present invention encompasses a
method for improving enhanced uplink performance during soft
handoff for a communication device in a UMTS communication system.
The method includes steps of defining code bits that uniquely
identify a particular mobile station; applying the code bits to a
downlink ACK/NAK transmission that can be received by a plurality
of mobile stations; discriminating between ACK/NAK transmissions
meant for the particular mobile station and ACK/NAK transmissions
meant for other mobile stations using the code bits from the
applying step; and utilizing the information in the ACK/NAK
transmission coded for the particular mobile station in an uplink
transmission.
The present invention may be more fully described with reference to
FIGS. 3 7. FIG. 4 is a block diagram of a communication system 1000
in accordance with an embodiment of the present invention.
Preferably, communication system 1000 is a Code Division Multiple
Access (CDMA) communication system, such as cdma2000 or Wideband
CDMA (WCDMA) communication system, that includes multiple
communication channels. Those who are of ordinary skill in the art
realize that communication system 1000 may operate in accordance
with any one of a variety of wireless communication systems, such
as a Global System for Mobile communication (GSM) communication
system, a Time Division Multiple Access (TDMA) communication
system, a Frequency Division Multiple Access (FDMA) communication
system, or an Orthogonal Frequency Division Multiple Access (OFDM)
communication system.
Similar to communication system 100, communication system 1000
includes multiple cells (seven shown). Each cell is divided into
multiple sectors (three shown for each cell--sectors a, b, and c).
A base station subsystem (BSS) 1001 1007 located in each cell
provides communications service to each mobile station located in
that cell. Each BSS 1001 1007 includes multiple base stations, also
referred to herein as base transceiver stations (BTSs), which
wirelessly interface with the mobile stations located in the
sectors of the cell serviced by the BSS. Communication system 1000
further includes a radio network controller (RNC) 1010 coupled to
each BSS, preferably through a 3GPP TSG UTRAN Iub Interface, and a
gateway 1012 coupled to the RNC. Gateway 1012 provides an interface
for communication system 1000 with an external network such as a
Public Switched Telephone Network (PSTN) or the Internet.
Referring now to FIGS. 3 and 4, communication system 1000 further
includes at least one mobile station (MS) 1014. MS 1014 may be any
type of wireless user equipment (UE), such as a cellular telephone,
a portable telephone, a radiotelephone, or a wireless modem
associated with data terminal equipment (DTE) such as a personal
computer (PC) or a laptop computer. Note that MS, UE, and user are
used interchangeably throughout the following text. MS 1014 is
serviced by multiple base stations, or BTSs, that are included in
an Active Set associated with the MS. MS 1014 wirelessly
communicates with each BTS in communication system 1000 via an air
interface that includes a forward link (from the BTS to the MS) and
a reverse link (from the MS to the BTS). Each forward link includes
multiple forward link control channels, a paging channel, and
traffic channel. Each reverse link includes multiple reverse link
control channels, a paging channel, and a traffic channel. However,
unlike communication system 100 of the prior art, each reverse link
of communication system 1000 further includes another traffic
channel, an Enhanced Uplink Dedicated Transport Channel (EUDCH),
that facilitates high speed data transport by permitting a
transmission of data that can be dynamically modulated and coded,
and demodulated and decoded, on a sub-frame by sub-frame basis.
Communication system 1000 includes a soft handoff (SHO) procedure
by which MS 1014 can be handed off from a first air interface whose
quality has degraded to another, higher quality air interface. For
example, as depicted in FIG. 4, MS 1014, which is serviced by a BTS
servicing sector b of cell 1, is in a 3-way soft handoff with
sector c of cell 3 and sector a of cell 4. The BTSs associated with
the sectors concurrently servicing the MS, that is, the BTSs
associated with sectors 1-b, 3-c, and 4-a, are the Active Set of
the MS. In other words, MS 1014 is in soft handoff (SHO) with the
BTSs 301, 303, and 304, associated with the sectors 1-b, 3-c, and
4-a servicing the MS, which BTSs are the Active Set of the MS. As
used herein, the terms `Active Set` and `serving,` such as an
Active Set BTS and a serving BTS, are interchangeable and both
refer to a BTS that is in an Active Set of an associated MS.
Furthermore, although FIGS. 3 and 4 depict BTSs 301, 303, and 304
as servicing only a single MS, those who are of ordinary skill in
the art realize that each BTS 301 307 may concurrently schedule,
and service, multiple MSs, that is, each BTS 301 307 may
concurrently be a member of multiple Active Sets.
FIG. 3 depicts a network architecture 300 of communication system
1000 in accordance with an embodiment of the present invention. As
depicted in FIG. 3, communication system 1000 includes multiple
BTSs 301 307, wherein each BTS provides a wireless interface
between a corresponding BSS 1001 1007 and the MSs located in a
sector serviced by the BTS. Preferably, a scheduling function 316,
an ARQ function 314 and a SHO function 318 are distributed in each
of the BTSs 301 307. RNC 1010 is responsible for managing mobility
by defining the members of the Active Set of each MS serviced by
communication system 1000, such as MS 1014, and for coordinating
multicast/multireceive groups. For each MS in communication system
1000, Internet Protocol (IP) packets are multi-cast directly to
each BTS in the Active Set of the MS, that is, to BTSs 301, 303,
304 in the Active Set of MS 1014.
Preferably, each BTS 301 307 of communication system 1000 includes
a SHO function 318 that performs at least a portion of the SHO
functions. For example, SHO function 318 of each BTS 301, 303, 304
in the Active Set of the MS 1014 performs SHO functions such as
frame selection and signaling of a new data indicator. Each BTS 301
307 can include a scheduler, or scheduling function, 316 that
alternatively can reside in the RNC 110. With BTS scheduling, each
Active Set BTS, such as BTSs 301, 303, and 304 with respect to MS
1014, can choose to schedule the associated MS 1014 without need
for communication to other Active Set BTSs based on scheduling
information signaled by the MS to the BTS and local interference
and SNR information measured at the BTS. By distributing scheduling
functions 306 to the BTSs 301 307, there is no need for Active Set
handoffs of a EUDCH in communication system 1000. The ARQ function
314 and AMC function, which functionality also resides in RNC 110
of communication system 100, can also be distributed in BTSs 301
307 in communication system 1000. As a result, when a data block
transmitted on a specific Hybrid ARQ channel has successfully been
decoded by an Active Set BTS, the BTS acknowledges the successful
decoding by conveying an ACK to the source MS (e.g. MS 1014)
without waiting to be instructed to send the ACK by the RNC
1010.
In order to allow each Active Set BTS 301, 303, 304 to decode each
EUDCH frame, MS 1014 conveys to each Active Set BTS, in association
with the EUDCH frame, modulation and coding information,
incremental redundancy version information, HARQ status
information, and transport block size information from MS 1014,
which information is collectively referred to as transport format
and resource-related information (TFRI). The TFRI only defines rate
and modulation coding information and H-ARQ status. The MS 1014
codes the TFRI and sends the TFRI over the same frame interval as
the EUDCH (accounting for the fact that the frame boundaries of the
TFRI and EUDCH may be staggered).
For example, as is known in the art, during reverse link
communications, the MS 1114 transmits frames to a plurality of BTSs
301, 303, 304. The structure of the frames, includes: (a) a flush
bit which indicates to the BTS when to combine a current frame with
a previously stored frame or to flush the current buffer; (b) data;
(c) a cyclic redundancy check (CRC) bit which indicates whether a
frame decoded successfully or not (i.e., whether the frame
contained any errors); and (d) a tail bit for flushing the channel
decoder memory. The received information contained in the frame is
referred to herein as soft information. The BTSs can combine frames
from multiple re-transmissions using an H-ARQ scheme.
After receiving a frame from the MS 1114, the BTSs 301, 303, 304
will process the frame and communicate to the MS 1114 over a
forward control channel whether the frame contained any errors. If
all BTSs communicate that the frame contains errors, the MS 1114
will retransmit the same frame to all BTSs, with the flush bit
cleared to instruct the BTSs to combine the retransmitted frame
with the original stored frame. If at least one of the BTSs
communicates that the frame contains no errors, the MS 1114 will
transmit the next frame to all the BTSs with the flush bit set to
instruct all BTSs to erase the previous frame from memory and not
to combine the previous frame with the current frame. The MS cannot
address individual non-scheduling BTSs, but only the scheduling
BTS, because the MS does not know which code channel to listen to
from the other non-scheduling Active Set BTSs. The problem is
solved in the present invention.
In a first, preferred embodiment of the present invention, a
specific code or codeword is applied to each ACK/NAK transmission
on the downlink ACK/NAK code channel. This specific codeword (or
color code) uniquely identifies a particular MS, such that if the
MS decodes an ACK/NAK transmission intended for another MS (i.e.
having the wrong color or codeword) it will decode it as a NAK.
This type of transmission identification discrimination is enabled
by specifying adequate inter-codeword distance (specified as a
Hamming distance or any other, well-known information-theoretic
measure) between an ACK codeword to one MS and the ACK codeword
transmitted to other MS's. A very simple example is to map NAK to
the zero or null location of the modulation constellation (see
FIGS. 6 and 7). Specifically, at channel assignment, the MS is
allocated two sets 320 of ACK/NAK channels for each BTS in the
Active Set (sets are updated when the Active Set is updated). One
set is used by the MS when the BTS is the scheduling BTS and the
other set is used when the BTS is a non-scheduling BTS.
The MS includes an ACK/NAK code channel indicator in the uplink
rate assignment (e.g. TFRI) control channel (also called E-DCCH)
which is received by all best serving Active Set BTS's.
In one embodiment only the non-scheduling Active Set BTS's read and
use the (SHO) ACK/NAK code channel indicator. (Note that it is
known in the art that the ACK/NAK channel for the scheduling Active
Set BTS is already indicated in the downlink scheduling assignment
message (SAM)). During SHO the MS chooses a ACK/NAK channel from
the allocated separate pool of ACK/NAK code channels and this is
indicated by the MS (using the ACK/NAK code channel indicator) for
use by the non-scheduling Active Set BTSs. In other words, a pool
of multiple (e.g. two) ACK/NAK code channels is used when the BTS
is the scheduling BTS, and a separate (non-scheduling) pool of
multiple (e.g. two) ACK/NAK code channels is used for
non-scheduling BTSs, In the case when more than one Active Set BTS
schedules the MS, the MS will know which ACK/NAK channel to listen
to (from the scheduling ACK/NAK channel pool) from each BTS due to
the ACK/NAK channel bit on each downlink scheduling assignment
message (SAM). If the selected scheduling sub-frame assignment is
different, then the MS will still know on which ACK/NAK
transmission intervals from each BTS ACK/NAK channel to listen.
By the MS assigning the ACK/NAK code channel to the non-scheduling
Active Set BTS's the MS then knows which ACK/NAK code channel to
listen to during SHO allowing macro-selection diversity benefit to
be obtained. In other words, the MS can detect ACKs from the
non-scheduling cell and move on to the next packet for
transmission. Although there can still be ACK/NAK code channel
assignment errors from the SHO MS's perspective at the
non-scheduling BTS's, the impact is not significant because the
only error condition that would cause significant impact (NAK
interpreted as ACK) is eliminated due to the color coding of the
ACK/NAK based on the MS identifier (ID).
In an alternative embodiment, all of the Active Set BTSs use the
ACK/NAK code channel indicator for choosing the appropriate ACK/NAK
channel from the separate non-scheduling ACK/NAK code channel
set.
In another embodiment, a color code based on the selected
scheduling BTSs unique ID is applied to the uplink TFRI message
such that the BTS's can determine whether it is selected or not.
This avoids the UE simultaneous scheduling problem. All BTSs would
have to still be able to decode the TFRI which would increase
probability of error due to each Active Set BTS having to elected
between many possible color codes.
Finally, in another embodiment the SSDT (site selection diversity
transmit) cell ID code bits can be used to indicate which BTS's
scheduling assignment message was selected.
In operation, FIG. 5 shows a message flow diagram 400 illustrates
an exchange of communications between an MS of communication system
1000, such as MS 1014, and each of the multiple BTSs included in an
Active Set of the MS, that is, BTSs 301, 303, and 304. MS 1014
communicates scheduling information 402 to each Active Set BTS 301,
303, 304 using a first reverse link control channel 406 with a
known fixed modulation and coding rate and transport block size. A
corresponding code assignment for the first reverse link control
channel is done on a semi-static basis. Preferably, MS 1014 does
not transmit control information when the MS's corresponding data
queue is empty.
Each Active Set BTS 301, 303, 304 receives scheduling information
402 from the MS 1014 serviced by the BTS via the first reverse link
control channel 406. The scheduling information 402 may include the
data queue status and the power status of the MS. Based on the
scheduling information 402 received from each MS serviced by a BTS,
each serving, or Active Set, BTS 301, 303, 304 schedules one or
more of the MSs serviced by the BTS, that is, MS 1014, for each
scheduling transmission interval 410.
Each Active Set BTS 301, 303, 304 uses reverse link interference
level, MS scheduling information 402, and power control information
to determine a maximum allowed power margin target or limit for
each MS 1014 serviced by the BTS. Power margin may be defined as
the difference between a current DPCCH power level and the maximum
power level supported by the MS. Or it may be defined as the
difference between a current DPCCH power level and the maximum
allowed EUDCH power level. The reverse link pilot is used for
demodulation purposes such as automatic frequency control,
synchronization, and power control. For example, in a WCDMA system
the reverse link pilot is carried on the reverse link DPCCH.
Finally, power margin can also be defined as in the equation below:
P.sub.margin=P.sub.eudch=P.sub.max-P.sub.dpcch(1+.beta..sub.dpdch+.beta..-
sub.hs-dpcch) (1) where .beta..sub.hs-dpcch is the power ratio of
HS-DPCCH/DPCCH. The high speed dedicated physical control channel
(HS-DPCCH) is a physical channel introduced for HSDPA in 3GPP
Release 5. It carries the Channel Quality Indicator (CQI)
information and ACK/NAK information to support H-ARQ and fast
scheduling and rate assignment), and .beta..sub.dpdh=DPDCH/DPCCH
power ratio.
Upon choosing an MS (e.g. MS 1014) to be scheduled, each Active Set
BTS 301, 303, 304 conveys a scheduling assignment 418 to the chosen
MS, such as MS 1014, on a first forward link control channel 426.
The first forward link control channel 426 can use the 10 ms frame
format depicted in FIG. 5, which format includes a scheduling
assignment 418, tail bits, and a CRC. Alternatively, the first
forward link control channel 426 frame size may use a frame format
of 2 ms. The first forward link control channel 426 may be
staggered to avoid additional latency. The scheduling assignment
418 consists of the maximum allowed `power margin` limit or target
and a map of the allowed EUDCH sub-frame transmission intervals,
such as a 2 ms sub-frame interval, for the next 10 ms transmission
interval (also known as the scheduling interval) using a first
forward link control channel 426. Note that a map is not needed if
the transmission interval is the same as the sub-frame transmission
interval.
Each Active Set BTS 301, 303, 304 also uses the second forward link
control channel 420 to convey ACK/NAK information to the MS related
to the MS's EUDCH sub-frame transmissions, in accordance with the
present invention and as previously described. Each MS 1014, is
assigned a unique identifier (ID) by the RNC that is used to
generate the `color` coding for that MS. The BTS applies the color
code of the MS to the ACK/NAK information for that MS.
In particular, FIGS. 6 and 7 show ACK/NAK coherent BPSK or QPSK
code assignments given color coded ACK/NAK transmissions, where
color coding is based on the MS's ID. During SHO, if an MS decodes
an ACK/NAK channel intended for another user then the mismatch in
color code would result in low correlation upon decoding which
would then be interpreted as a NAK. Even though a separate pool of
ACK/NAK channels is used during SHO by the non-scheduling Active
Set BTSs there is a chance of contention since these channels are
shared among multiple MS's in SHO. The asynchronous nature of
uplink timing will also help reduce the likelihood of collision on
ACK/NAK channel assignments, as will be described below.
An MS in a SHO region, such as MS 1014, may receive one or more
scheduling assignments 418 from one or more Active Set, or serving,
BTSs 301, 303, 304. When the MS receives more than one scheduling
assignment, the MS may select a scheduling assignment 418
corresponding to the best rate. The best rate could be the one
which represents the highest uplink data rate or the best rate
could represent the highest data rate which produces acceptable
interference levels at all BTSs. The MS determines the TFRI for
each EUDCH sub-frame 422 based on the interference information
(maximum allowed power margin limit) from the selected scheduling
assignment 418 and the current scheduling information 402 measured
at the MS, that is, current buffer occupancy and power status or
power margin. The MS uses a fast power control function and the
feedback rate is performed on a slot-by-slot basis, for example,
1500 Hz in the case of 3GPP UMTS. The MS then transmits the EUDCH
sub-frame 422 to the Active Set BTSs 301, 303, 304 using the
determined TFRI.
When a MS 1014 receives a ACK/NAK transmission it uses the
information to determine uplink transmission activity. For example,
if a ACK is received the MS does not need to retransmit the
corresponding packet. If a NACK is received the MS will retransmit
the corresponding packet upon receiving a subsequent scheduling
assignment if in explicit scheduling mode otherwise it will
retransmit the packet at an appropriate time when in autonomous
mode.
FIG. 7 shows that asynchronous timing on uplink reduces likelihood
of ACK/NAK channel assignment collisions. Note that ACK/NAK
transmission for UE1 are almost time orthogonal with those from UE2
in this example due to asynchronous timing between UEs (MSs) and
the chosen uplink scheduling transmission assignments. Hence, even
if the ACK/NAKs for different UEs were sent on the same channel
(which is not always possible in this example because of
transmission overlap) the contention would be reduced.
Although the above solution is preferred, there are other
techniques encompassed by the present invention that can also be
used with other compromises. Therefore, in a second embodiment of
the present invention, ACK/NAK information or scheduling assignment
information are transported on the associated downlink physical
control channel (DPCH), which is code efficient and avoids SHO
complexity, but also degrades other services carried on the
associated DPCH channel.
In this case, a new field is proposed on the downlink associated
DPCH to carry scheduling assignment messages and HARQ ACK/NAK
information for explicit scheduling and to carry persistence
information and HARQ ACK/NAK for autonomous scheduling to support
the enhanced uplink. Alternatively, the coded bits can be punctured
on the DPCH. The new DPCH field is called the EU field. The EU
field is DTX'ed by the non-scheduling Active Set BTSs during SHO.
Simultaneous scheduling by Active Set BTSs poses no problems. New
downlink slot formats are created by taking bits from the DPDCH
Ndata 2 field and/or the DPCCH pilot field to create the EU field.
Alternatively, bits can be taken from the DPDCH Ndata 1 field to
form the EU field. Layer 1 signaling data chosen to be sent on the
new EU field are optimized to as few bits as possible and can be
mapped to 2 ms, 4 ms, 5 ms, 6 ms, 10 ms or larger frame sizes which
helps reduce the number of channels (N) required for N channel
Stop&Wait HARQ due to timing constraints.
When an MS (UE) is explicitly scheduled (Explicit mode) to use the
enhanced uplink channel (E-DCH) a scheduling assignment message
(SAM) is required to be sent by the scheduling BTS to the UE on a
scheduling assignment channel. Note that E-DCH and EUDCH are used
interchangeably in the following text. Also a downlink channel is
required to signal an acknowledgement or negative acknowledgement
by the BTS to the UE for each received transmission. This downlink
channel is called the ACK/NAK channel. It is also possible to
incorporate the ACK/NAK transmission into the SAM.
Several bearer options exist for sending the SAM and ACK/NAK
information: (1) separate code channels for SAM and ACK/NAK (2 or
10 ms E-DCH frame size or transmission time interval (TTI)); (2)
separate code channel for combined SAM and ACK/NAK (2 or 10 ms
E-DCH TTI); (3) rate match SAM on downlink associated DPCH by using
10 ms TTI (10 ms E-DCH); (4) separate DPCCH field on downlink
associated DPCH for SAM (2 or 10 ms E-DCH); (5) separate DPCCH
field on downlink associated DPCH for ACK/NAK (2 or 10 ms E-DCH);
and (6) reuse TFCI split mode for indicating ACK/NAK information on
the downlink associated DPCH (10 ms E-DCH).
The first option is the most flexible but is the most code
inefficient and requires the UE to have knowledge of which ACK/NAK
code channel to listen during soft handoff (SHO) from the
non-scheduling Active Set BTSs. Another advantage is that it is
more flexible with respect to voice services during SHO. The second
option helps reduce code inefficiency over the first option 1 but
flexibility is lost requiring perhaps larger N for N-channel
Stop-and-wait HARQ protocol. The third option is code efficient but
really only works if the E-DCH TTI is 10 ms and only works if UE is
not in soft handoff since in SHO there is no inter-BSS
communication or there may not even be inter-BTS communication and
demodulation and decoding at the UE is done after soft combining
occurs. The TFCI indicates whether SAM is rate matched (only when
not in SHO). Also the serving BTS needs to know UE's SHO state. The
fourth option is code efficient and could work for any size TTI
including both 2 or 10 ms E-DCH. During SHO, all the other
non-scheduling Active Set BTS's must DTX the SAM field. Also, the
serving BTS needs to know UE's SHO state. A solution could be used
to signal each Active Set BTS the SHO state change of a UE when new
BTS is added or dropped. The fifth option is code efficient and
flexible and avoids the ACK/NAK SHO code channel problem but
impacts speech or other services carried on the associated DPCH and
is similar to the fourth option. The sixth option is code efficient
but really only works if the E-DCH TTI is 10 ms or larger and
requires that a larger power offset be used for the TFCI field.
Only fifteen bits are made available by splitting the TFCI for 10
ms DPCH. Hence, the sixth option is really only useful for
transferring ACK/NAK information.
The fourth and fifth options can be considered further. If a UE is
to use the E-DCH in this implementation, then a slot format
downlink channel reconfiguration is performed such that each DPCCH
slot always includes a new DPCCH field called the EU field, which
is created by taking away bits from the adjacent Data 2 DPDCH
field. When a BTS is not scheduling the UE to use the E-DCH it
DTX's the EU field. Alternatively, the TFCI can be used to indicate
if the EU field is present by employing a hard TFCI split. That is,
one TFCI bit (EU indication bit) out of one of the slots per frame
or sub-frame is used to indicate the presence or absence of the EU
field while the other bits in each TFCI field of the remaining
slots per frame or sub-frame are still used to represent the TFCI.
This EU indication bit is only used when the EU is not in soft
handoff otherwise during SHO it is either DTX'ed by all Active Set
BTSs or not used at all such that no split TFCI is used during SHO.
In any event the EU field is always present during SHO but DTX'ed
by the non-scheduling Active Set BTSs.
When the UE is not in soft handoff mode, rate matching can be used.
Rate matching occurs over whole 10 ms frames in the 3GPP downlink.
If the sub-frame period is 2 ms, then the rate matching algorithm
will not know in advance which slots contain the EU field.
Therefore the rate matching must assume a fixed value for Ndata 2.
The output of the rate matching algorithm will then be punctured or
repeated on a slot by slot basis in order to create the EU field in
the required slots. For instance, the Data 2 bits can be punctured
if the EU field is present, where the rate matching for the DPDCH
assumes a slot format with zero length EU field. Alternatively, the
rate matching for the DPDCH could assume that the EU field is
always present and some Data 2 bits could get repeated if the EU
data is in fact not present which could be more reliable. Something
in between is also possible. For example, if N.sub.EU=8, then the
rate matching for DPDCH could assume a value for Data 2 such that
if EU is present four data bits get punctured, else if EU is not
present four data bits get repeated. In this case the Data 2 value
assumed by rate matching would be mid way between the actual Data 2
values when EU is and is not present. In any case, the EU
indication bit then indicates whether the EU field is present or
not i.e. it indicates whether the channel bits are Data 2 bits or
EU bits.
FIG. 9 shows the prior art details of the SAM and ACK/NAK
associated DPCH bearer for the fourth and fifth options. The
information carried in the SAM is: (1) maximum power margin limit
(or rate limit or TFCS limit), four bits; (2) bit map (if
scheduling multiple frame or sub-frame intervals), one bit for each
interval; and (3) ACK/NAK code channel code assignment (if separate
code channel), two bits. The downlink DPCH frame structure is given
as {[ND1],[TPC],[TFCI],[ND2],[Pilot]}.
In accordance with the present invention, a new set of downlink
DPCH slot formats are required with a new DPCCH field to carry the
ACK/NAK and SAM information is given as
{[ND1],[TPC],[TFCI],[ND2],[EU],[Pilot]} and as shown in FIG. 10.
This ACK/NAK+SAM field or EU field takes bits away from the Data 2
field as shown in Table 1 below, which shows the DPDCH and DPCCH
fields.
TABLE-US-00001 TABLE 1 DPDCH and DPCCH fields Channel Transmitted
Slot Channel Symbol DPDCH DPCCH slot per radio Format Bit Rate Rate
Bits/ Bits/Slot Bits/Slot frame #i (kbps) (ksps) SF Slot
N.sub.Data1 N.sub.Data2 N.sub.EU N.sub.TPC N.sub.- TFCl N.sub.Pilot
N.sub.Tr 0 15 7.5 512 10 0 4 0 2 0 4 15 0A 15 7.5 512 10 0 4 0 2 0
4 8 14 0B 30 15 256 20 0 8 0 4 0 8 8 14 1 15 7.5 512 10 0 2 0 2 2 4
15 1B 30 15 256 20 0 4 0 4 4 8 8 14 2 30 15 256 20 2 14 0 2 0 2 15
2A 30 15 256 20 2 14 0 2 0 2 8 14 2B 60 30 128 40 4 28 0 4 0 4 8 14
2C 30 15 256 20 2 6 8 2 0 2 15 3 30 15 256 20 2 12 0 2 2 2 15 3A 30
15 256 20 2 10 0 2 4 2 8 14 3B 60 30 128 40 4 24 0 4 4 4 8 14 3C 30
15 256 20 2 6 6 2 2 2 15 3D 30 15 256 20 2 13 0 2 2 1 15 3E 30 15
256 20 2 6 7 2 2 1 15 3F 30 15 256 20 2 5 8 2 2 1 15 3G 30 15 256
20 2 7 6 2 2 1 15 3H 30 15 256 20 2 10 2 2 2 2 15 3I 30 15 256 20 2
9 3 2 2 2 15 3J 30 15 256 20 2 8 4 2 2 2 15 3K 30 15 256 20 2 11 2
2 2 1 15 3L 30 15 256 20 2 10 3 2 2 1 15 3M 30 15 256 20 2 9 4 2 2
1 15 4 30 15 256 20 2 12 0 2 0 4 15 4A 30 15 256 20 2 12 0 2 0 4 8
14 4B 60 30 128 40 4 24 0 4 0 8 8 14 4C 30 15 256 20 2 6 8 2 0 2 15
4D 30 15 256 20 2 14 0 2 0 2 15 4E 30 15 256 20 2 12 2 2 0 2 15 4F
30 15 256 20 2 11 3 2 0 2 15 4G 30 15 256 20 2 10 4 2 0 2 15 4H 30
15 256 20 2 10 2 2 0 4 15 4I 30 15 256 20 2 9 3 2 0 4 15 4J 30 15
256 20 2 8 4 2 0 4 15 5 30 15 256 20 2 10 0 2 2 4 15 5A 30 15 256
20 2 8 0 2 4 4 8 14 5B 60 30 128 40 4 20 0 4 4 8 8 14 6 30 15 256
20 2 8 0 2 0 8 15 6A 30 15 256 20 2 8 0 2 0 8 8 14 6B 60 30 128 40
4 16 0 4 0 16 8 14 7 30 15 256 20 2 6 0 2 2 8 15 7A 30 15 256 20 2
4 0 2 4 8 8 14 7B 60 30 128 40 4 12 0 4 4 16 8 14 8 60 30 128 40 6
28 0 2 0 4 15 8A 60 30 128 40 6 28 0 2 0 4 8 14 8B 120 60 64 80 12
56 0 4 0 8 8 14 8C 60 30 128 40 6 18 10 2 0 4 8 14 9 60 30 128 40 6
26 0 2 2 4 15 9A 60 30 128 40 6 24 0 2 4 4 8 14 9B 120 60 64 80 12
52 0 4 4 8 8 14 9C 60 30 128 40 6 20 6 2 2 4 15 9D 60 30 128 40 6
19 7 2 2 4 15 9E 60 30 128 40 6 18 8 2 2 4 15 9F 60 30 128 40 6 17
9 2 2 4 15 9G 60 30 128 40 6 16 10 2 2 4 15 9H 60 30 128 40 6 18 10
2 2 2 15 9I 60 30 128 40 6 19 9 2 2 2 15 9J 60 30 128 40 6 20 8 2 2
2 15 9K 60 30 128 40 6 21 7 2 2 2 15 9L 60 30 128 40 6 22 6 2 2 2
15 9M 60 30 128 40 6 28 0 2 2 2 15 9N 60 30 128 40 6 24 2 2 2 4 15
9O 60 30 128 40 6 23 3 2 2 4 15 9P 60 30 128 40 6 22 4 2 2 4 15 10
60 30 128 40 6 24 0 2 0 8 15 10A 60 30 128 40 6 24 0 2 0 8 8 14 10B
120 60 64 80 12 48 0 4 0 16 8 14 11 60 30 128 40 6 22 0 2 2 8 15
11A 60 30 128 40 6 20 0 2 4 8 8 14 11B 120 60 64 80 12 44 0 4 4 16
8 14 11C 60 30 128 40 6 18 8 2 2 4 15 11D 60 30 128 40 6 26 0 2 2 4
15 11E 60 30 128 40 6 20 2 2 2 8 15 11F 60 30 128 40 6 22 4 2 2 8
15 12 120 60 64 80 12 48 0 4 8* 8 15 12A 120 60 64 80 12 40 0 4 16*
8 8 14 12B 240 120 32 160 24 96 0 8 16* 16 8 14
In this table the new slots formats proposed by the present
invention and slot formats 2C, 3C 3M, 4C 4J, 8C, 9C 9P and 11C
11F.
The present invention also envisions the possibility of puncturing
one to three Data bits in each slot, and accumulating the necessary
information over a frame (2 ms). However, this technique may have a
high error and latency, and is restricted to three bits per
slot.
While the present invention has been particularly shown and
described with reference to particular embodiments thereof, it will
be understood by those skilled in the art that various changes may
be made and equivalents substituted for elements thereof without
departing from the scope of the invention as set forth in the
claims below. Accordingly, the specification and figures are to be
regarded in an illustrative rather then a restrictive sense, and
all such changes and substitutions are intended to be included
within the scope of the present invention.
Benefits, other advantages, and solutions to problems have been
described above with regard to specific embodiments. However, the
benefits, advantages, solutions to problems, and any element(s)
that may cause any benefit, advantage, or solution to occur or
become more pronounced are not to be construed as a critical,
required, or essential feature or element of any or all the claims.
As used herein, the terms "comprises," "comprising," or any
variation thereof, are intended to cover a non-exclusive inclusion,
such that a process, method, article, or apparatus that comprises a
list of elements does not include only those elements but may
include other elements not expressly listed or inherent to such
process, method, article, or apparatus.
* * * * *